Magnetic media with improved exchange coupling

ABSTRACT

A magnetic recording medium includes a substrate, an underlayer, a lower magnetic layer formed on the underlayer, an intermediate layer, and an upper magnetic layer formed on the intermediate layer. The intermediate layer is typically Ru, and promotes antiferromagnetic coupling between the upper and lower magnetic layers. The upper and lower magnetic layers are typically Co alloys. The lower magnetic layer has a high saturation magnetization Ms to promote high exchange coupling between the upper and lower magnetic layers. The dynamic coercivity of the lower magnetic layer is lower than the exchange field to ensure rapid switching of the lower magnetic layer.

BACKGROUND OF THE INVENTION

[0001] This invention pertains to magnetic recording media such asmagnetic disks.

[0002]FIG. 1 illustrates a magnetic recording medium 1 constructed inaccordance with the prior art used for longitudinal data recording.Medium 1 comprises a substrate 2, an underlayer 3, a Co alloy magneticlayer 4 and a carbon protective overcoat 5. Also shown in FIG. 1 is afirst region 4 a of layer 4 magnetized in a first direction D1, a secondregion 4 b magnetized in a second direction D2 opposite the firstdirection, and a transition region TR between regions D1 and D2. Inmagnetic recording, it is desirable for transition region TR to be assmall as possible in order to maximize areal recording density. Ingeneral, the length of transition region TR is proportional to MrT/Hc,where Mr is the magnetic remanence of the Co alloy, T is the thicknessof layer 4, and Hc is the coercivity of layer 4.

[0003] In order to reduce the length of region TR, one might be temptedto reduce MrT. Unfortunately, reducing MrT in medium 1 reduces thethermal stability of layer 4. In other words, reducing MrT reduces theability of layer 4 to retain its magnetization state, and hence the datarecorded in layer 4, as temperature increases. (Obviously, thermalstability is a highly desirable characteristic in a magnetic medium.)

[0004]FIG. 2 illustrates a second magnetic recording medium 20 inaccordance with the prior art comprising a substrate 22, an underlayer24, a lower Co alloy magnetic layer 26, a Ru layer 28, an upper Co alloymagnetic layer 30 and a carbon protective overcoat 32. Medium 20 isdesigned to facilitate simultaneous reduction of the length oftransition region TR and increase in thermal stability. In particular,if Ru layer 28 has a thickness within a certain range (e.g. 0.3 to 1.0μm), magnetic layers 26 and 30 are antiferromagnetically coupled to oneanother. Because of this, the length of transition region TR for medium20 is proportional to Mr₂₆T₂₆−KMr₃₀T₃₀, where K is a proportionalityconstant, Mr₂₆ is the magnetic remanence of layer 26, T₂₆ is thethickness of layer 26, Mr₃₀ is the magnetic remanence of layer 30 andT₃₀ is the thickness of layer 30. (Constant K is related to the degreeof antiferromagnetic coupling between layers 26 and 30.) However, thethermal stability of medium 20 increases as a function ofMr₂₆T₂₆+K₂Mr₃₀T₃₀. Thus, while the antiferromagnetic coupling permitsone to reduce the length of transition region TR, it also improvesthermal stability. (The antiferromagnetic coupling also improves thesignal to noise ratio of medium 20.) When recording data in medium 20 ofFIG. 2, because of the antiferromagnetic coupling between layers 26 and30, when one magnetizes a region within layer 30, e.g. as shown by arrowD3, the magnetization direction of layer 26 is in the oppositedirection, e.g. as shown by arrow D4. FIG. 3 shows a hysteresis loop 40for the structure of FIG. 2 if layers 26 and 30 were strongly coupled.As can be seen, as one increases the applied magnetic field H_(app) tomedium 20, in portion P1 of hysteresis loop 40, both magnetic layers 26and 30 are magnetized in the same direction D3. As one reduces theapplied magnetic field H_(app) past point P2, the magnetizationdirection of layer 26 begins to switch to direction D4. Portion P3 ofhysteresis loop 40 shows the magnetic characteristics of medium 20 aslayer 26 changes magnetization direction in response to applied magneticfield H_(app). As applied magnetic field H_(app) is brought to zero(point P4), layer 26 is magnetized in direction D4.

[0005]FIG. 4 shows a hysteresis loop of medium 20 if layer 26 wereweakly antiferromagnetically coupled to layer 30. As can be seen, thepoint P5 at which layer 26 switches magnetization direction (i.e. fromdirection D3 to D4) occurs at a much lower applied magnetic fieldH_(app) in FIG. 4 than in FIG. 3. Weak coupling between layers 26 and 30is disadvantageous because it increases the amount of time required toswitch the state of medium 20 to an antiferromagnetic state. Inparticular, it takes more time to create a situation in which layer 30is magnetized in direction D3 and layer 26 is magnetized in directionD4. The magnetic recording medium relies on thermal energy to switch themagnetization direction of layer 26 to direction D4. Further, weakcoupling can also create a situation in which layer 26 is not ascompletely magnetized as desired when H_(app) is brought to zero.

[0006] It would be desirable to increase antiferromagnetic couplingbetween layers 26 and 30. One way to do this is to add pure Co layers 34and 36 on each side of Ru layer 28, e.g. as provided in medium 20′ shownin FIG. 5. Co layers 34 and 36 increase antiferromagnetic couplingbetween layers 26 and 30. Unfortunately, Co layers 34 and 36 increasenoise in medium 20′ because of intergranular magnetic coupling in layers34 and 36. It would be highly desirable to increase antiferromagneticcoupling between layers 26 and 30 without suffering this increase innoise.

SUMMARY

[0007] A magnetic recording medium in accordance with the inventioncomprises a lower magnetic layer, an intermediate layer above the lowermagnetic layer, and an upper magnetic layer above the intermediatelayer. The recording medium is typically a magnetic disk. The upper andlower magnetic layers are ferromagnetic, and typically comprise a Coalloy, a Fe alloy or a Ni alloy. The intermediate layer has thecharacteristic that it induces antiferromagnetic coupling between theupper and lower magnetic layers. In one embodiment, the intermediatelayer comprises Ru.

[0008] In accordance with one aspect of the invention, the lowermagnetic layer has a high Ms in order to facilitate a high exchangefield Hex. (The exchange field is a measure of the amount of couplingbetween the upper and lower magnetic layers.) In one embodiment, the Msof the lower magnetic layer is greater than or equal to 250 emu/cm³, andtypically greater than 300 emu/cm³. The Ms of the lower magnetic layercan be less than or equal to 2000 emu/cm³ and generally less than orequal to 1400 emu/cm³.

[0009] It has been discovered that the high Ms values cooperate with theRu intermediate layer to provide strong antiferromagnetic coupling. (Itis believed that the reason that a high Ms promotes antiferromagneticcoupling is that coupling is a function of the density of spinsavailable for transport across the Ru. The higher the Ms, the greaterthe spin density, the higher the amount of exchange across the Ru.)

[0010] In accordance with another aspect of the invention, the relationbetween dynamic coercivity Hc and the exchange field Hex is such thatthe lower magnetic layer will reach its steady state magnetizationcondition after writing within one period of revolution of the magneticdisk. In one embodiment, the lower magnetic layer will reach between 90and 100% of its steady state magnetization condition within one periodof revolution of the magnetic disk. In another embodiment, the lowermagnetic layer will reach between 95 and 100% of its steady statemagnetization condition within one period of revolution of the magneticdisk.

[0011] Hc of the lower magnetic layer is greater than or equal to zerobut less than the exchange field Hex at recording switching times. TheHe of the lower magnetic layer at recording switching times is typicallyless than or equal to about one half of the exchange field for recordingtimes. This facilitates quickly switching the lower magnetic layer toits desired magnetization direction. (The Hc of the upper magnetic layerat recording switching times is typically substantially greater than theHc of the lower magnetic layer at recording switching times.)

[0012] In accordance with another feature of the invention, theanisotropy constant Ku of the upper magnetic layer is greater than0.5×106 ergs/cm³ to provide good thermal stability. In one embodiment,the Ku of the upper layer is greater than 1.0×10⁶ ergs/cm³. (The Ku ofthe upper magnetic layer should not be so high as to hamper writing, andis typically less than 10⁷ ergs/cm³.) The Ku of the lower layer can besmaller than the Ku of the upper layer. For example, the lower magneticlayer can have a Ku of 1.0×10⁴ ergs/cm³, 1.0×10³ ergs/cm³, or even lower(but greater than or equal to 0 ergs/cm³). (A lower Ku for the lowermagnetic layer facilitates a lower coercivity, which in turn facilitatesease of switching the magnetization direction of the lower magneticlayer.) In one embodiment, the lower magnetic layer is a Co based alloycomprising between 5 and 20 at. % Cr, 0 to 6 at. % Ta, 0 to 10 at. % Band 0 to 10 at. % Pt. The alloy can contain between 0 and 10 at. % X,where X is one or more other elements. In one embodiment, X is one ormore of Nb, Ta, Cu, Mo, W, V, Si, C, Pd, Ru, Ir or Y. Preferably, thisalloy exhibits a Ms, Hc and Ku as described above.

[0013] In one embodiment, the upper magnetic layer is a Co based alloycomprising between 10 and 30 at. % Cr, 8 to 20 at. % Pt and 0 to 20 at.% B. The upper magnetic layer can comprise between 0 and 10 at. % X,where X is one or more other elements. X can be one or more of Nb, Ta,Cu, Mo, W, V, Si, C, Pd, Ru, Ir or Y. Again, preferably the alloyexhibits a Hc and Ku as described above.

[0014] A magnetic recording medium in accordance with another embodimentof the invention comprises two or more Ru interlayers (e.g. two, threeor more interlayers), each sandwiched between two magnetic layers. Theuppermost magnetic layer has the same characteristics as described abovefor the upper magnetic layer. The magnetic layers below the Ruinterlayers have the same characteristics as described above for thelower magnetic layer.

[0015] Although the foregoing description refers to upper and lowermagnetic layers, either or both of the upper and lower magnetic layerscan comprise a plurality of sublayers of different compositions. Thus,for example, if the lower layer comprises a plurality of sublayers, theeffective composite Ms of the sublayers combined should be a value asdescribed above. Similarly, if the upper or lower layer comprises aplurality of sublayers, the effective composite dynamic Hc (e.g. atrecording times) and Ku of the sublayers should be a value as describedabove.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 illustrates in cross section a first magnetic recordingmedium constructed in accordance with the prior art.

[0017]FIG. 2 illustrates in cross section a second magnetic recordingmedium constructed in accordance with the prior art comprising a Rulayer for facilitating antiferromagnetic coupling between upper andlower magnetic Co alloy layers.

[0018]FIG. 3 is a hysteresis loop for a magnetic recording medium ifupper and lower magnetic layers were strongly antiferromagneticallycoupled to one another.

[0019]FIG. 4 is a hysteresis loop for a magnetic recording medium ifupper and lower magnetic layers were weakly antiferromagneticallycoupled to one another.

[0020]FIG. 5 illustrates in cross section a third magnetic recordingmedium constructed in accordance with the prior art comprising a Colayer formed between magnetic Co alloy layers and a Ru layer.

[0021]FIG. 6 illustrates in cross section a magnetic recording mediumconstructed in accordance with a first embodiment of the invention.

[0022]FIG. 7 illustrates in cross section a magnetic recording medium inaccordance with a second embodiment of the invention.

[0023]FIG. 8A illustrates the effect of H-Field Sweep Rate on MrT in amagnetic recording medium in which the lower magnetic film has an Ms of300 emu/cm³.

[0024]FIG. 8B illustrates the effect of H-Field Sweep Rate on MrT for amagnetic recording medium in which the lower magnetic film has an Ms of550 emu/cm³ and therefore a higher exchange field than that of FIG. 8A.

[0025]FIG. 9A illustrates the fundamental harmonic amplitude decay for amagnetic recording medium in which the exchange field is about 300 Oe.

[0026]FIG. 9B illustrates the fundamental harmonic amplitude decay for amagnetic recording medium in which the exchange field is about 2500 Oe.

[0027]FIG. 10 illustrates a magnetic recording medium constructed inaccordance with third embodiment of the invention.

[0028]FIG. 11 illustrates a magnetic recording medium constructed inaccordance with a fourth embodiment of the invention.

[0029]FIG. 12 illustrates a magnetic disk in accordance with the presentinvention incorporated into a disk drive.

DETAILED DESCRIPTION

[0030] Referring to FIG. 6, a magnetic recording medium 100 inaccordance with the invention comprises a non-magnetic substrate 102, anunderlayer 104, a lower magnetic layer 106, an intermediate layer 108,an upper magnetic layer 110 and a carbon protective overcoat 112.Substrate 102 can be an aluminum alloy substrate coated with anelectroless plated nickel-phosphorus alloy. Alternatively, substrate 102can be glass, glass-ceramic, or other appropriate material. (Typically,the above-mentioned layers are formed on both the top and bottomsurfaces 102 a, 102 b of substrate 102, but only the layers on topsurface 102 a are shown for ease of illustration.) Magnetic layers 106and 110 are typically Co, Fe or Ni-based alloys. Layer 106 is typicallybetween 2 and 8 nm thick, and layer 110 is typically 6 to 30 nm thick.Intermediate layer 108 is typically Ru or a Ru alloy (e.g. consistingessentially of Ru). (Layer 108 is typically between 0.3 and 1.0 nmthick.) For the case of Co alloys, layers 106 and 110 typically have aHCP crystal structure and a 11 {overscore (2)} 0 orientation.

[0031] Underlayer 104 is typically Cr or a Cr alloy such as Cr—Mo. Inone embodiment, underlayer 104 comprises Cr₈₀Mo₂₀ (at. %), has athickness of 10 nm, and a BCC crystal structure.

[0032] As mentioned above, in accordance with one aspect of theinvention, magnetic recording medium 100 exhibits a high exchange fieldHex. This is typically accomplished (at least in part) by ensuring thatmagnetic layer 106 exhibits a high Ms, preferably greater than or equalto 250 emu/cm³, and typically greater than or equal to 300 emu/cm³, andin one embodiment, greater than 350 emu/cm³. Typically, the Ms of layer106 is less than 2000 emu/cm³ and for the case in which layer 106comprises primarily Co, the Ms of layer 106 is less than about 1400emu/cm³. (While the lower magnetic layer 106 can have a higher Ms thanupper magnetic layer 110, upper magnetic layer 110 typically has ahigher magnetic moment MsT (magnetization times thickness) than lowermagnetic layer 106.)

[0033] Also as mentioned above, the coercivity Hc of layer 106 istypically greater than or equal to zero but less than the exchange fieldHex at recording switching times. The recording switching time is theamount of time one exposes a point on the recording medium to a writemagnetic field. For the case of a magnetic disk in a disk drive duringrecording, the recording switching time is approximately the amount oftime it takes a point on the spinning disk to travel the length of thehead write gap. (Disks in currently manufactured disk drives spin at arate between about 4,000 and 15,000 rpm. This corresponds to a period ofrotation of 15 milliseconds to 4 milliseconds.) For disk drivescurrently being produced, the switching time is about 10 ns. Coercivityis the strength of the magnetic field applied to a magnetized region ofa magnetic film that is required to reduce the magnetization of thatregion to zero. (It is a measure of the field strength needed to recorddata in the film.) Coercivity depends on the length of time one appliesthe magnetic field to a region of the magnetic film. In other words, itrequires a stronger magnetic field to write to a magnetic film if thefield is only applied to the film for a very short time than if thefield is applied to the film for a very long time. In one embodiment,the coercivity of lower magnetic layer 106 at recording switching timesis less than the exchange field Hex of medium 100, and preferably lessthan or equal to one half of exchange field Hex (e.g. for a recordingswitching time of 100 ns or less). Typically, the above-mentionedcondition holds true for switching times of 1 ns to 10 ns or less (orgenerally between 100 picoseconds and 100 ns). This facilitates theswitching of the magnetization layer 106 to a direction opposite that oflayer 110. (Optionally, the above-mentioned coercivity condition mayalso hold true for other amounts of time that a write field is appliedto a region of medium 100.)

[0034] In one embodiment, upper layer 110 has a static coercivitygreater than 3000 Oe (but typically less than 10,000 Oe). Lower layer106 has a static coercivity less than 2500 Oe (but typically greaterthan or equal to 0 Oe).

[0035] Upper layer 110 has a dynamic coercivity (e.g. for switchingtimes of 10 ns or less) between 6000 and 25,000 Oe. Lower layer 106 hasa dynamic coercivity less than 2500 Oe (but typically greater than orequal to 0 Oe).

[0036] Magnetic layer 106 is typically a HCP Co alloy. In oneembodiment, layer 106 has 5 to 20 at. % Cr, 0 to 6 at. % Ta, 0 to 10 at.% B, 0 to 10 at. % Pt, and the balance is Co. For example, layer 108 canbe CoCr₁₆Ta₄. (As used herein, CoCr₁₆Ta₄ means an alloy comprising 16at. % Cr, 4 at. % Ta, and the remainder Co.) Alternatively, layer 106can have 0 to 10 at. % X, where X is one or more other elements, e.g.one or more of Cu. Mo, W, V, Si, C, Pd, Ru, Ir or Y. Layer 106 can havea Ku greater than or equal to 1.0×10⁴ ergs/cm³, e.g. between 0.5×10 and1.0×10⁶ ergs/cm³.

[0037] In an alternative embodiment, lower magnetic layer 106 can beanother magnetically soft material with intergranular decoupling, e.g.suitably modified NiFe (permalloy), FeAlSi (sendust), CoTaZr, FeTaC,NiFeNb, CoFe, NiCrFe, NiV, CuNi, FeRh or PtMn.

[0038] Magnetic layer 110 is also typically a Co alloy layer and has ahigh Ms. In one embodiment, layer 110 has between 10 and 30 at. % Cr, 8to 20 at. % Pt, 0 to 20 at. % B and the balance Co. For example, layer110 can be CoCr₁₅Pt₁₁B₁₁. Alternatively, layer 110 can also include 0 to10 at. % X, where X is one or more other elements, e.g. one or more ofNb, Ta, Cu, Mo, W, V, Si, C, Pd, Ru, Ir or Y. In one embodiment, layer110 has a high Ku, e.g. a Ku greater than about 1.0×10⁶ erg/cm³, e.g.between 1.0×10⁶ and 1.0×10⁴ erg/cm³ to promote thermal stability. (TheKu of layer 110 is greater than that of layer 106.) Layer 110 also has ahigh Ms, e.g. greater than 300 emu/cm³. In one embodiment, layer 110 hasa Ms between 300 and 650 emu/cm³.

[0039]FIGS. 8A and 8B illustrate the effect of H-Field Sweep-Rate on MrTfor magnetic recording media with lower and higher Ms, respectively. Inparticular, the H_(app)-field sweep rate for FIGS. 8A and 8B variedbetween 0.1 seconds to several seconds. The magnetic disk of FIG. 8B hada lower magnetic layer exhibiting an Ms of about 550/cm³. Because ofthis, antiferromagnetic coupling between the upper and lower magneticlayers was relatively high, and the lower magnetic layer generallyswitched magnetization directions before the applied field H_(app)reached 0 Oe. In other words, Mr was generally independent of the sweeprate.

[0040] In contrast, the lower magnetic layer of FIG. 8A had a lower Ms(300 emu/cm³) and thus exhibited less antiferromagnetic coupling.Therefore, in the context of the magnetic medium of FIG. 8A (with alower level Hc close to the exchange field strength), Mr was moredependent on sweep rate-an undesirable characteristic because it doesnot allow the lower layer to switch quickly to the desired state.

[0041]FIGS. 9A and 9B illustrate the fundamental harmonic amplitudedecay for magnetic recording media with an exchange coupling field Hexof 300 Oe and 2500 Oe, respectively. The Y axis of FIGS. 9A and 9Brepresents the normalized fundamental harmonic amplitude. In otherwords, after data is recorded in the magnetic recording medium, theamplitude of the recorded signal is repeatedly read back. The Y axisrepresents subsequent read-back values divided by the initial read-backvalue. Data in FIG. 9A was generated for different data recordingdensities. As can be seen, the extent to which amplitude dropped overtime was highly dependent on recording density. For example, for adensity of 3 kFCI (3000 flux changes per inch), over a 20 second timeperiod, the normalized fundamental harmonic amplitude dropped toapproximately 0.73, whereas for a density of 289 kFCI, the normalizedfundamental harmonic amplitude only dropped to a value of about 0.98after 20 seconds. The reason for this difference is that thedemagnetizing field increases as recording density increases (i.e. asthe size of a magnetized region decreases). This demagnetizing fieldhelps to switch the magnetization direction in lower magnetic layer 106.If the demagnetizing field is small 12 (as in the case of a lowrecording density), it provides less assistance in switching themagnetization direction of magnetic layer 106, and therefore it takesmagnetic layer 106 more time to settle into a final magnetization state(i.e. magnetized in direction D4).

[0042] As mentioned above, the data of FIG. 9A was generated for a diskexhibiting relatively low antiferromagnetic coupling between the upperand lower magnetic layers, e.g. for an exchange field of about 300 Oe.In FIG. 9B, the disk exhibited relatively high antiferromagneticcoupling between the upper and lower magnetic layers, i.e. about 2500Oe. This relatively high coupling promotes switching of themagnetization direction of the lower magnetic layer 106. Therefore, evenfor fairly low recording densities (e.g. 3 kFCI), the normalizedfundamental harmonic amplitude after 20 seconds is about 0.91, comparedto 0.73 for FIG. 9A. A significant change in normalized fundamentalharmonic amplitude is undesirable because it means that medium 100 mayexhibit inadequate switching and signal stability.

[0043]FIG. 7 illustrates a magnetic recording medium 100 a constructedin accordance with another embodiment of the invention. Medium 100 a issimilar to medium 100 of FIG. 6, but includes an optional seed layer 105formed between underlayer 104 and lower magnetic layer 106. Seed layer105 can be as discussed in U.S. Pat. No. 6,150,015, issued to Bertero etal. on Nov. 21, 2000, incorporated herein by reference.

[0044] Also shown in FIG. 7 is a magnetic layer 120 formed on magneticlayer 110. Magnetic layer 120 enables one to tailor medium 100 a withenhanced flexibility so that it exhibits desired Hc, MrT, noise or PW50.In the embodiment of FIG. 7, layer 120 can be 10 nm thick, and cancomprise CoCr₂₄Pt₁₂B₈, while layer 110 can be 6 nm thick and compriseCoCr₁₅Pt₁₁B₁₂. Alternatively, magnetic layer 120 could comprise anotheralloy such as CoCrPtTaB, other Co alloys, a Ni alloy or a Fe alloy.

[0045]FIG. 10 illustrates a magnetic recording medium in accordance withanother embodiment of the invention. In FIG. 10, a medium 100 bcomprises substrate 102, a 8 nm thick Cr—Mo₂₀ underlayer 104, a 2 nmthick CoCr₂₅Ta₂ seed layer 105, a 4 nm thick CoCr₁₆Ta₄ magnetic layer106, a 0.8 nm thick Ru intermediate layer 108, magnetic sublayers 110 a,110 b and 110 c and a protective overcoat 112. Merely by way of example,sublayers 110 a, 110 b and 110 c can be 2 nm thick CoCr₁₆Ta₄, 6 nm thickCoCr₂₃Pt₁₁B₅Ta₁ and 6 nm thick CoCr₁₅Pt₁₀B₁₂. In this embodiment,sublayers 110 a, 110 b, and 110 c (which make up upper magnetic layer110) are magnetized in a first direction, while lower magnetic layer 106is magnetized in a second direction opposite the first direction byvirtue of antiferromagnetic coupling resulting from intermediate layer108. Thus, it is seen that the upper magnetic layers can comprise aplurality of sublayers. In an alternative embodiment, lower layer 106can also comprise a plurality of sublayers.

[0046] In this patent, the term “layer structure” will refer to astructure comprising one layer or a plurality of layers that areferromagnetically coupled to one another. Thus, as used herein, lowerlayer 106 is a layer structure, and layers 110 a, 110 b and 110 ccollectively are a layer structure.

[0047]FIG. 11 illustrates a medium 100 c comprises a lowermost magneticlayer 106′, a lower Ru layer 108′, a magnetic layer 106″, a Ru layer108″ an uppermost magnetic layer 110 and a protective overcoat 112. Forthe embodiment of FIG. 11, the magnetic characteristics of layer 110 areas described above for the embodiments of 6, 7 and 10. Ru layers 108′and 108″ are typically between 0.3 and 1.0 nm thick, and facilitate theabove-described antiferromagnetic coupling phenomenon. Layers 106′ and106″ have the same magnetic characteristics as those described above forlayer 106 in the embodiments of FIGS. 6, 7 and 10. If one writes data inlayer 110 such that the magnetization direction is D5 and then removesthe applied write magnetic field H_(app), the magnetization direction inlayer 106″ will be direction D6, which is in the opposite direction ofD5. The magnetization direction in layer 106′ will be direction D7,which is the opposite of direction D6.

[0048] While FIG. 11 shows two Ru layers 108′, 108″ sandwiched betweenmagnetic layers, in other embodiments, three or more Ru layers can beprovided, each sandwiched between magnetic layers. The benefit of thisembodiment is to create greater thermal stability in medium 100 c.

[0049] In the embodiments of FIGS. 6, 7, 10 and 11, the magnetizationdirection in layer 106 (or layers 106′ and 106″ for the case of FIG. 11)is controlled by the magnetization direction in layer 110. Inparticular, layer 110 is antiferromagnetically coupled to layer 106 (orto layer 106″ for the case of FIG. 11) and the magnetization in layer110 forces layer 106 (106″) to assume a magnetization direction that isopposite to the direction of layer 110. Similarly, the antiferromagneticcoupling between layers 106′ and 106″ cause layer 106′ to have amagnetization direction that is opposite to the magnetization directionof layer 106″. In effect, the magnetization directions for layers 106,106′ and 106″ are determined by the magnetization direction of layer110. Thus, it can be said that layers 106, 106′ and 106″ are “slavelayers”, i.e. layers whose steady state magnetization direction (afterthe write field has been removed) is determined either directly orindirectly by a “master layer”, e.g. layer 110.

[0050] Magnetic recording media in accordance with the invention aretypically manufactured using a vacuum deposition technique such assputtering. For example, one or more substrates can be placed in asubstrate carrier that carries the substrates past a set of sputteringtargets to deposit the various layers of the magnetic disk. The targetshave compositions that are substantially the same as the composition ofthe layers that they are used to produce. Sputtering is typicallyaccomplished in an atmosphere comprising an inert gas such as argon.(Other gases may be present in the sputtering chamber as well.) Amagnetic medium in accordance with the invention (e.g. medium 100, 100a, 100 b or 100 c) is typically in the form of a disk incorporatedwithin a disk drive, e.g. disk 200 drive 201 (FIG. 11). Disk drive 201comprises magnetic disk 200 mounted on a spindle 202 which is coupled toa motor 204 for rotating disk 200. A pair of read-write heads 206 a, 206b are positioned proximate to disk 200 for reading data from and writingdata to magnetic layers on each side of disk 200. Heads 206 a, 206 b aremounted on suspensions 208 a, 208 b, which in turn are mounted onactuators (e.g. rotary or linear actuators 210 a, 210 b) for movingheads 206 a, 206 b over desired data recording tracks of disk 200.Although only one disk 200 is shown in drive 201, drive 201 can containmultiple disks.

[0051] While the invention has been described with respect to specificembodiments, those skilled in the art will recognize that changes can bemade in form and detail without departing from the spirit and scope ofthe invention. For example, the disk substrate can be textured, e.g.using mechanical, chemical, and/or laser texturing techniques. Differenttypes of protective overcoats (e.g. carbon, hydrogenated or nitrogenatedcarbon, or zirconia) can be applied to upper magnetic layer 110. Alubricant can be applied to the top surface of the disk (e.g. aperfluoropolyether lubricant). The various layers of the magnetic diskcan be formed by any of a number of deposition techniques, e.g. a vacuumdeposition technique such as sputtering. Different segregants can beadded to one or more of the magnetic layers to break exchange couplingbetween the grains, e.g. boron, silica, alumina, zirconia, or otheroxides such as tantalum oxide, cobalt oxide, etc. Different magneticlayer thicknesses can be employed. Different aspects or features of theinvention can be practiced independently of one another. Accordingly,all such changes come within the invention.

We claim:
 1. A magnetic recording medium comprising: a substrate; alower magnetic layer structure formed over said substrate, said lowermagnetic layer structure exhibiting a Ms greater than 250 emu/cm³; anintermediate layer comprising Ru; and an upper magnetic layer structureformed over said intermediate layer, said upper magnetic layer structurebeing antiferromagnetically coupled to the lower magnetic layerstructure.
 2. Magnetic recording medium of claim 1 wherein the Ms of thelower magnetic layer structure is greater than 300 emu/cm³.
 3. Magneticrecording medium of claim 1 wherein said lower magnetic layer structurecomprises a layer comprising mostly Co, between 5 and 20 at. % Cr, 0 to6 at. % Ta, 0 to 10 at. % B and 0 to 10 at. % Pt.
 4. Magnetic recordingmedium of claim 3 wherein said layer of said lower magnetic layerstructure comprises between 0 and 10% X, where X is one or more elementsother than Co, Cr, Ta, B or Pt.
 5. Magnetic recording medium of claim 4wherein X comprises one or more of Nb, Ta, Cu, Mo, W, V, Si, C, Pd, Ru,Ir or Y.
 6. Magnetic recording medium of claim 1 wherein the uppermagnetic layer structure comprises a layer comprising mostly Co, between10 and 30 at. % Cr, between 8 and 20 at. % Pt, and 0 to 20 at. % B. 7.Magnetic recording medium of claim 6 wherein said layer of said uppermagnetic layer structure comprises between 0 and 10 at. % X, wherein Xis one or more elements other than Co, Cr, Pt or B.
 8. Magneticrecording medium of claim 7 wherein X comprises one or more elementsselected from Nb, Ta, Cu, Mo, W, V, Si, C, Pd, Ru, Ir or Y.
 9. Themagnetic recording medium of claim 1 further comprising an underlayerformed between the substrate and the lower magnetic layer structure. 10.The magnetic recording medium of claim 1 wherein at least one of saidupper and lower magnetic layer structures comprise a plurality oflayers.
 11. The magnetic recording medium of claim 1 wherein a lowestmagnetic layer structure is formed above said substrate, a secondintermediate layer comprising Ru is formed between said lowest magneticlayer structure and said lower magnetic layer structure, and said lowestmagnetic layer structure is antiferromagnetically coupled to said lowermagnetic layer structure.
 12. A magnetic disk drive comprising themagnetic recording medium of claim
 1. 13. A magnetic disk comprising: asubstrate; a lower magnetic layer structure formed over the substrate;an intermediate layer comprising Ru; an upper magnetic layer structureformed over the intermediate layer, said upper magnetic layer structurebeing antiferromagnetically coupled to the lower magnetic layerstructure, wherein the relationship between the dynamic coercivity ofthe lower magnetic layer structure and the exchange field is such thatduring writing a portion of the lower magnetic layer structure achievessubstantially its steady magnetization state within the time requiredfor one revolution of said disk.
 14. The magnetic disk of claim 13wherein at least one of said upper and lower magnetic layer structurescomprise a plurality of layers.
 15. The magnetic disk of claim 13wherein a lowest magnetic layer structure is formed above saidsubstrate, a second intermediate layer comprising Ru is formed betweensaid lowest magnetic layer structure and said lower magnetic layerstructure, and said lowest magnetic layer structure isantiferromagnetically coupled to said lower magnetic layer structure.16. Magnetic disk of claim 13 wherein said magnetic disk is incorporatedinto a disk drive, said magnetic disk rotating.
 17. A magnetic diskcomprising: a substrate; a lower magnetic layer structure formed overthe substrate; an intermediate layer comprising Ru; and an uppermagnetic layer structure formed over the intermediate layer, said uppermagnetic layer structure being antiferromagnetically coupled to thelower magnetic layer structure, wherein the relationship between thedynamic coercivity of the lower magnetic layer structure and theexchange field is such that during writing a portion of the lowermagnetic layer structure achieves more than 90% of its steadymagnetization state within the time required for one revolution of saiddisk.
 18. A magnetic disk comprising: a substrate; a lower magneticlayer structure formed over the substrate; an intermediate layercomprising Ru; and an upper magnetic layer structure formed over theintermediate layer, said upper magnetic layer structure beingantiferromagnetically coupled to the lower magnetic layer structure,wherein the relationship between the dynamic coercivity of the lowermagnetic layer structure and the exchange field is such that duringwriting a portion of the lower magnetic layer structure achieves morethan 95% of its steady magnetization state within the time required forone revolution of said disk.
 19. A magnetic recording medium comprising:a substrate; a lower magnetic layer structure formed over the substrate;an intermediate layer comprising Ru; and an upper magnetic layerstructure formed over the intermediate layer, said upper magnetic layerstructure being antiferromagnetically coupled to the lower magneticlayer structure, wherein the relationship between the dynamic coercivityof the lower magnetic layer structure and the exchange field is suchthat during writing a portion of the lower magnetic layer structureachieves substantially its steady magnetization state within 100milliseconds.
 20. A magnetic recording medium comprising: a substrate; alower magnetic layer structure formed over the substrate; anintermediate layer comprising Ru; and an upper magnetic layer structureformed over the intermediate layer, said upper magnetic layer structurebeing antiferromagnetically coupled to the lower magnetic layerstructure, wherein the relationship between the dynamic coercivity ofthe lower magnetic layer structure and the exchange field is such thatduring writing a portion of the lower magnetic layer structure achievesmore than 90% of its steady magnetization state within 100 milliseconds.21. A magnetic recording medium comprising: a substrate; a lowermagnetic layer structure formed over the substrate; an intermediatelayer comprising Ru; and an upper magnetic layer structure formed overthe intermediate layer, said upper magnetic layer structure beingantiferromagnetically coupled to the lower magnetic layer structure,wherein the relationship between the dynamic coercivity of the lowermagnetic layer structure and the exchange field is such that duringwriting a portion of the lower magnetic layer structure achieves morethan 95% of its steady magnetization state within 100 milliseconds. 22.Magnetic recording medium comprising: a substrate; a lower magneticlayer structure formed over said substrate, said lower magnetic layerstructure having a Ku between 0 and 10⁶ erg/cm³; an intermediate layercomprising Ru formed over the lower magnetic layer structure; and anupper magnetic layer structure formed over said intermediate layer, saidupper magnetic layer structure being antiferromagnetically coupled tosaid lower magnetic layer structure and having a Ku greater than 10⁶erg/cm³.
 23. Magnetic recording medium of claim 22 wherein said lowermagnetic layer structure has a Ku less than 0.5×106 erg/cm³.
 24. Themagnetic recording medium of claim 22 wherein at least one of said upperand lower magnetic layer structures comprise a plurality of layers. 25.The magnetic recording medium of claim 22 wherein a lowest magneticlayer structure is formed above said substrate, a second intermediatelayer comprising Ru is formed between said lowest magnetic layerstructure and said lower magnetic layer structure, and wherein saidlowest magnetic layer structure is antiferromagnetically coupled to saidlower magnetic layer structure.
 26. A magnetic disk drive comprising themagnetic recording medium of claim
 22. 27. A magnetic recording mediumcomprising: a lower magnetic layer structure; an intermediate layercomprising Ru formed over the lower magnetic layer structure; and anupper magnetic layer structure antiferromagnetically coupled to thelower magnetic layer structure and formed over said intermediate layer,the dynamic coercivity of the lower magnetic layer structure beinggreater than or equal to zero but less than the exchange field betweenthe upper and lower magnetic layer structures.
 28. Magnetic recordingmedium of claim 27 wherein said dynamic coercivity of said lowermagnetic layer structure is less than one half of the exchange field.29. Magnetic recording medium of claim 27 wherein said dynamiccoercivity is for a recording switching time between 1 and 10 ns. 30.The magnetic recording medium of claim 27 wherein at least one of saidupper and lower magnetic layer structures comprise a plurality oflayers.
 31. The magnetic recording medium of claim 27 wherein a lowestmagnetic layer structure is formed above said substrate, a secondintermediate layer comprising Ru is formed between said lowest magneticlayer structure and said lower magnetic layer structure, and said lowestmagnetic layer structure is antiferromagnetically coupled to said lowermagnetic layer structure.
 32. A magnetic disk drive comprising themagnetic recording medium of claim
 27. 33. Magnetic recording mediumcomprising: a substrate; a lower magnetic layer structure formed oversaid substrate; an intermediate layer comprising Ru formed over saidlower magnetic layer; and an upper magnetic layer structure formed oversaid intermediate layer, said upper magnetic layer beingantiferromagnetically coupled to said lower magnetic layer structure,the coercivity of said lower magnetic layer structure as measured in aswitching time of 10 milliseconds being less than the exchange fieldbetween said upper and lower magnetic layer structures.
 34. Magneticrecording medium of claim 33 wherein said coercivity of said lowermagnetic layer structure as measured in a switching time of 10milliseconds is less than one half of the exchange field between saidupper and lower magnetic layer structures.
 35. The magnetic recordingmedium of claim 33 wherein at least one of said upper and lower magneticlayer structures comprise a plurality of layers.
 36. The magneticrecording medium of claim 33 wherein a lowest magnetic layer structureis formed above said substrate, a second intermediate layer comprisingRu is formed between said lowest magnetic layer structure and said lowermagnetic layer structure.
 37. A magnetic disk drive comprising themagnetic recording medium of claim
 33. 38. Magnetic recording mediumcomprising: a substrate; a lower magnetic structure formed over saidsubstrate, said lower magnetic structure comprising a magnetically softmaterial with intergranular decoupling; an intermediate layer comprisingRu formed over said lower magnetic layer structure; and an uppermagnetic layer structure formed over said intermediate layer, said uppermagnetic layer structure being antiferromagnetically coupled to saidlower magnetic layer structure.
 39. Magnetic recording medium of claim38 wherein said lower magnetic layer structure comprises an alloyselected from the list consisting of permalloy, sendust, CoTaZr, FeTaC,NiFeNb, CoFe, NiCrFe, NiV, CuNi, FeRh and PtMn.